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First round of voting takes place April 23

Contest too tight to call going into final week

Paris (CNN)It has been one of the most unpredictable and dramatic presidential campaigns in French political history -- and with less than a week to go before the election, the outcome remains too close to call.

Only a few weeks ago, it appeared almost guaranteed that the French electorate would vote for a face off between National Front Leader Marine Le Pen and independent candidate Emmanuel Macron.

But as Sunday's first round of voting draws ever closer, the political whirlwind that is far-left candidate Jean-Luc Mélenchon appears to be gathering speed.

Marine Le Pen

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Le Pen is intensifying her anti-immigration rhetoric, telling a crowd at the Zenith arena Monday night that her first move as president would be to impose a temporary ban on legal immigration to France.

"I will set up a moratorium on all legal immigration to stop this delirium, this uncontrolled situation," she said.

The National Front leader gave a similar message to supporters Sunday, telling the crowd of about 5,000 people she would "reinstate France's borders."

When she mentioned the European Union, the crowd booed, and she repeated her vow to take France out of the bloc, as well as from the border-free Schengen area.

A charismatic speaker who is popular with younger voters, his easy conversational style has won over supporters.

He's the left's best shot at beating the far-right in the second round -- and he also offers something the French electorate is craving: change.

But that same offering may be his undoing, with his policies unlikely to appeal to all voters.

Mélenchon advocates withdrawing from NATO and the International Monetary Fund. He also wants to renegotiate EU rules, and calls for a referendum on whether France should leave bloc if the rules are not changed.

Raising the minimum wage and strictly limiting the work week to 35 hours are other goals of his campaign.

François Fillon

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Republican candidate Fillon is still hanging in there, despite a campaign thrown off track by scandal.

Fillon, 63, is under investigation on multiple counts, including embezzlement of public funds.

His problems started when French newspaper Le Canard Enchainé reported that his wife and two of his adult children earned nearly €1 million ($1.08 million) as parliamentary assistants, but allegedly never performed any work in the jobs.

The candidate has rejected the claims, saying his wife Penelope, who has also been charged, worked for 15 years as his deputy and handled several roles, including managing his schedule and representing him at cultural events. He also said his daughter and son were employed in similar positions for 15 months and six months respectively, which he said is not illegal, but was an "error of judgment."

While the allegations have harmed his campaign, he remains in the race, albeit with only an outside chance of a top-two finish.

CNN's James Masters wrote from London, with Maud Le Rest and Margaux Deygas reporting from Paris